Patrick Harvie is set to penalise owners of fossil fuel boilers in a shake-up of energy efficiency standards under a “massive transition” to how people heat their homes.

The Greens minister has insisted that millions of homes will need to clean up heating systems “at a pace and scale that is consistent with Scotland’s legal climate targets”.

Scotland has pledged to cut 1990 levels of carbon emissions by 75% in just seven years’ time, while the nation has a legal net zero target of 2045, five years ahead of the UK.

One of the biggest challenges is replacing fossil fuel gas boilers in homes with climate-friendly heating-systems such as heat pumps, with Mr Harvie previously admitting the costs could total £33bn.

Read more: Scottish ministers propose gas boilers ban in new buildings from 2024

From 2025, certain trigger points such as the sale of a home, will mean properties will need to meet EPC band C energy efficiency standards, while new fossil fuel boilers will be banned in new buildings from next April.

Ahead of the shake-up, Mr Harvie is set to reform EPC standards so they are more appropriate for driving the improvements needed to reach net zero.

It is understood that this could include taking account of the type of heating system, raising the possibility of those with an old fossil fuel boilers receiving a lower rating than those who have installed a heat pump.

Currently, EPC ratings take account of how costly it is to heat a home, but the reforms could also include the fabric efficiency and the type of heating.

Read more: Patrick Harvie urged to reform 'not fit for purpose' energy standards

Statutory advisers, the Climate Change Committee (CCC), wrote to Mr Harvie in February, calling for an overhaul of the EPC system.

The body warned that domestic EPCs should be clearer and focus on four metrics – energy use intensity, fabric, heating system type and cost of heating.

Writing exclusively for the Herald on Sunday, the zero carbon buildings minister said his government wants “all homes to reach new energy efficiency standards by no later than 2033”.

He said: “Improved energy efficiency is essential but nowhere near enough.

“We can’t insulate our way to zero carbon buildings.

Read more: Patrick Harvie admits government 'decades behind' on renewable heating

“To do that we need to change the way we heat homes.

“To meet our 2030 targets alone, more than one million Scottish homes will need to change to a climate-friendly heating system: a massive transition – as big as the shift from coal to gas last century, but in a shorter timescale.”

The Scottish Government has introduced rules that mean from next April, newly-built homes and other buildings coming forward for a building warrant will need to have a green heating system installed.

Mr Harvie said: “Scotland’s construction industry is building the future we need right now.

“But, of course, the biggest challenge we face is bringing existing properties – 2.5 million homes, 100,000 other buildings – from fossil fuel heating to climate-friendly heating.”

The Greens co-leader said that “for most people”, the transition will mean “either a very energy-efficient heat pump or another modern form of electric heating”.

He added: “For some households, it will mean drawing on a heat network – systems of pipes used to transfer heat from one central source to nearby homes, schools or offices.

“My job is to support that kind of shift at a pace and scale that is consistent with Scotland’s legal climate targets.”

Read more: Two thirds of Scottish Government buildings fail energy targets

Mr Harvie has stressed that “in every country making this transition, regulation is needed to steer choices about energy use and heating systems”.

He said: “Scotland is no different.

“It’s what our manufacturers and installers need as well, with the prospect of thousands of skilled, secure jobs for decades ahead.”

The minister has insisted that “we are not asking households to make this transition by themselves”, amid concerns over costs.

He said: “The package of support provided by the Scottish Government is already the most generous in the UK.

“We updated the Home Energy Scotland scheme last December and we will be launching a new warmer homes Scotland scheme in the Autumn.

“We have provided specific funds for public buildings, heat networks and social landlords and I am excited by some of the plans I see coming forward.”

Read more: All homes in Scotland to meet energy standards from 2025 despite £33bn costs

Hr Harvie has previously stressed that around £33bn will be needed for Scotland’s buildings to install heating systems that meet net zero targets, the bulk set to come from the private sector.

His Greens co-leader and fellow government minister, Lorna Slater is drawing up an investment plan to lever in “responsible private finance” to plug a £20bn funding gap for nature.

The Herald revealed that former first minister Nicola Sturgeon was lobbying the City of London for investment to reach climate targets.

The Scottish Government is expected to publish the interim report from the green heat finance taskforce, a technical group set up to look at potential ways to fund the transition to net zero.

Mr Harvie has warned “the challenge is daunting but the prize is huge”.

He added: “Not just in making sure that Scotland meets the climate emergency head-on but in securing our energy future; providing the jobs and skills we need and making us all less vulnerable to volatile fossil fuel prices.

“We can’t do it entirely alone and the UK’s Climate Change Committee has highlighted that the UK Government must equally to rise to the challenge.

“But I am confident that Scotland has the ambition and the will to make it happen.”

In his letter to Mr Harvie in February, the outgoing chairman of the CCC, Lord Deben, warned that the present EPC ratings are “not fit for purpose”, adding that they “do not provide the clear information people need to understand the energy efficiency of their homes”.

Lord Deben and the CCC has suggested reformed EPCs to include six ranked categories for the type of heating system.

He said this would provide people “with a clear hierarchy of heating system types, giving clarity on the merits of different heating technologies”.

Scottish Conservative shadow net zero, energy and transport secretary Douglas Lumsden, said: “Patrick Harvie’s plans will be deeply concerning for homeowners reliant on gas boilers.

“The Green minister is typically acting like he knows best by ploughing ahead with these plans. This is hugely naïve considering he has put in a pitiful amount of the funding required to support homeowners to replace gas boilers.

“Penalising them during a cost-of-living crisis is simply unacceptable. While we all want to see a just transition, policies must be fair and measured.

“Patrick Harvie must be fully upfront about what his plans to overhaul these ratings will mean for homeowners in reality.”